GROZNY, April 15 (Reuters) - Around 18 people died on Monday in one of the biggest battles between rival pro-Kremlin factions in the restive Russian republic of Chechnya, a witness told Reuters on Tuesday.

Russia has fought two wars against Chechen insurgents since 1994, but over the last few years has ceded local power to former enemy warlords and their fighters, isolating a dwindling number of remaining rebels.

The Kremlin has now retrained and equipped thousands of former Chechen rebels, but tension and rivalry between the different forces remain high.

On Monday, soldiers loyal to Chechen president Ramzan Kadyrov clashed with forces supporting the former rebel commander Sulim Yamadayev in the town of Gudermes, in the east of the mainly Muslim republic.

Yamadayev is one of Kadyrov's main rivals and commands the biggest militia outside Kadyrov's control.

The battle occurred when convoys from each group ran into each other in the town, where Kadyrov also lives, and civilians were among the dead, according to the witness, who declined to be named. (Writing by James Kilner in Moscow; Editing by Kevin Liffey)

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